The present invention relates generally to ladders, and more particularly, is directed to an extension ladder that is fully foldable into a compact configuration.
A conventional extension ladder includes a lower ladder section and an upper ladder section arranged in parallel, sliding relation to each other. Each ladder section includes two elongated end rails connected together in a parallel, spaced apart relation by a plurality of transverse rungs.
The manner of slidably connecting the first and second ladder sections to each other may take various forms. For example, the upper ladder section may slide within the lower ladder section, as taught by U.S. Pat. No. 3,692,143 to Kummerlin et al and U.S. Pat. No. 4,376,470 to Ashton. Alternatively, the upper ladder section may be connected with the lower ladder section to slide adjacent thereto, for example, as taught by U.S. Pat. No. 745,320 to Bruno and U.S. Pat. No. 2,162,040 to Webster.
A problem, however, with conventional extension ladders is that the ladder sections are generally formed as continuous, non-folding straight sections. As a result, each ladder section has a substantial length. Because of this extensive length, a conventional extension ladder can, for all practical purposes, only be carried by a truck, van or the like. In other words, it is impractical to carry a conventional extension ladder in an automobile or the like.
In an attempt to overcome these shortcomings, foldable ladders, such as those shown in U.S. Pat. No. 3,143,185 to Wenger and U.S. Pat. No. 4,666,327 to Su, have recently gained in popularity. A conventional foldable ladder includes three or more foldable sections that are hinged together in end to end relation. Thus, the foldable sections can be folded between a fully extended position in which the foldable sections are arranged in-line, that is, in the same plane, and a compact storage position in which the foldable sections are provided in parallel, overlaying relation. In addition, various intermediate configurations can be achieved. In order to provide such movement between the in-line configuration and the fully folded configuration in which the foldable sections are provided in parallel, overlaying relation, the hinges are provided in alternating fashion on opposite sides of the ladder, as shown by U.S. Pat. No. 3,517,772 to Weis et al, so that the foldable sections are folded in a zig-zag manner between the fully extended in-line configuration and the compact fully folded storage position.
Although the hinges are conventionally provided in such alternating fashion, U.S. Pat. No. 3,006,432 to Gurley and U.S. Pat. No. 4,666,327 to Su each show a foldable ladder in which the hinges are provided on the same side of the ladder. However, the reason for such arrangement of the hinges is to place the ladder in the shown U-shaped configurations. Thus, all of the foldable sections cannot be folded in a parallel, overlaying relation for compact storage. As a result, transport of the ladder is difficult, since the ladder always occupies a large amount of space.
In any event, all of the aforementioned folding ladders present another problem. Specifically, the number of foldable sections that can be hinged together is limited. This is because, unlike a conventional extension ladder, a foldable ladder only has the thickness of a single ladder section for supporting a person. Thus, the foldable ladder becomes more and more unstable as the length of the foldable ladder increases. In other words, the greater the length of such a foldable ladder, the greater the bending and swaying of the foldable ladder when it is fully extended in the in-line configuration. For this reason, foldable ladders that are now sold are of limited length, for example, twelve to fourteen feet, or the like, which is much less than the length that can be achieved with a conventional extension ladder.
A hybrid ladder is also known, which includes an upper foldable ladder section and at least one lower non-foldable ladder section slidably connected with the upper foldable ladder section. An example of such a hybrid ladder in which the upper ladder section includes two foldable sections is shown in U.S. Pat. No. 4,376,470 to Ashton, while an example of such a hybrid ladder in which the upper ladder section includes four foldable sections is shown in U.S. Pat. No. 2,024,039 to Harting.
However, such a hybrid ladder, while being of a slightly greater length than a conventional foldable ladder, due to the addition of at least one lower non-foldable ladder section, is still limited in its length. This is due to the non-foldable nature of the lower ladder section.
In addition, it will be appreciated that with conventional foldable ladders, the largest bending of the ladder occurs in the middle of the ladder. This is because the lower end of the ladder is in contact with the ground and the opposite upper end of the ladder is in contact with the side of a building. This large bending does not occur with conventional extension ladders due to the fact that the upper and lower ladder sections thereof are connected at the middle of the ladder and thereby provide a double thickness and thereby a reinforcement thereat. With the hybrid ladders, each non-foldable ladder section is connected to a foldable end section of the foldable ladder section, so that, when extended in an in-line arrangement, the middle of the ladder is still of a single thickness, and thereby inherently weak.